1. Field of the Invention
The present invention relates to a tramway transit system in which vehicles having wheels equipped with for example rubber tires travel on a pre-established tramway, specifically relates to an actuator of an automatic steering mechanism of the vehicle.
2. Description of the Related Art
A vehicle supported by wheels with rubber tires for a new transit system is generally provided with guide wheels so that the vehicle is steered to travel along the tramway, the steering being usually done mechanically through the guide wheels engaging with a guide rail laid along the tramway.
The mechanical guide mechanism is superior in point of view of safety and reliability, however, structure of bogies to which the wheels and driving mechanism thereof are mounted inevitably becomes complicated, is increased in weight, and results in increased running cost. Further, it is necessary to lay down the guide rail having enough strength to support the guide rails all along the tramway with high accuracy, so vast amounts of construction cost of the tramway is needed.
In order to eliminate the above problem, a steering system not requiring a guide rail is proposed in Japanese Laid-Open Patent Application No. 2002-351544 (patent literature 1).
The steering system of a tramway vehicle disclosed in the patent literature 1 is composed such that a plurality of on-ground devices which memorize and send out information necessary for operation of the vehicle are laid down along the whole length of the track on which the vehicle travels, the control device installed on the vehicle emits signals based on the information sent out from the on-ground devices when the vehicle travels along the track, and the vehicle is steered by the steering device installed on the vehicle in accordance with the signals. With the steering system, a guide rail for steering the vehicle is not required, construction and maintenance costs can be reduced, and also vibration and noise are reduced.
The steering system of the patent literature 1 will be explained referring to FIGS. 13 and 14. FIG. 13a is a schematic side elevation of the conventional steering system, and FIG. 13b is a schematic front elevation thereof. FIG. 14 is a schematic plan view of the conventional steering system.
Referring to FIGS. 13a, 13b, reference numeral 03 is a vehicle used in the new tramway transit system, the vehicle 03 travels along a track 01. The vehicle 03 is supported on front and rear bogies 04 which supported by wheels with rubber tires 05 attached thereto. The wheels are driven by drive motors 06 and steered by actuators 07.
The steering system includes on-ground devices 02, a transmitter 09, a receiver 09, a control device 010, and a steering device 020. The vehicle is steered by turning the wheels 05. A plurality of non-exited on-ground devices 02 are laid down on the track 01 along whole length thereof at a predetermined spacing. Specific information is memorized in each of the on-ground devices. The specific information includes the discrimination number, position information, track information, and control information of the concerned on-ground device.
Position information (geographic site information) is information concerning the position of each on-ground device 02 such as the absolute coordinate point and distance from a reference point. Further, track information expressing conditions of the track at the site of each on-ground device such as the gradient, curvature, cant, ramification of the track are memorized in each of the on-ground device as necessary.
Although the on-ground devices 02 are not exited, i.e. have not been provided with power sources, emit signals of the information memorized upon receiving electric power. The on-ground device 02 has for example an electronic circuit including ROM for memorizing operation information.
The transmitter 08 is a device for feeding electric power by means of a radio wave. The receiver 09 is a device for receiving the operation information emitted from the on-ground device 02 when the device 02 has received the radio wave. The control device 010 is a device for performing prescribed processing based on the operation information the receiver 09 received and transmitting directive signal of speed and steering of the vehicle to the drive motor 06 and actuator 07.
Referring to FIG. 14, the steering device 020 is a device for turning the wheel 05 under the steering directive and comprises an electric or hydraulic or pneumatic actuator 07 connected to an end of an arm 011 of which the other end is supported for rotation by a pin 012 fixed to the bogie 04, a connecting rod 059, levers 056a and 056b for left and right wheel 05 respectively, and a tie rod 057 for connecting the levers.
When the actuator 07 is actuated by the steering directive from the control device 010, the arm 011 is rotated about the pin 012 and the levers 056a, 056b are turned via the connecting rod 059 and the tie rod 057 to turn the wheels 05 to the right or left.
According to the system, the vehicle 03 is steered based on operation information memorized in the on-ground devices 02 without using a guide rail, etc. Therefore, construction cost of the track 01 is decreased to a large extent because the guide rail, etc. is not needed. Further, as wear-out parts such as guide wheels are not used, maintenance cost is decreased. Also, occurrence of vibration and noise which will occur when the guide rail and guide wheels are provided due to the contact between them is eliminated.
However, according to the steering system disclosed in the patent literature 1, as mechanical steering by means of the guide rail and guide wheels is not provided, it is difficult to secure safety of vehicle traveling against runaway and running out of track when malfunction occurs in the steering system and under abnormal circumstances caused by strong wind, rainfall, snowfall, etc.
Further, there occur gradual deviations of the vehicle friction from the running course caused by changes in the road friction coefficient, the number of passengers, and wear of the tires, so it is necessary to correct such deviations in order to secure safe and efficient high speed traveling of the vehicle.
Therefore, in a tramway transit system in which a vehicle travels along a predetermined track under automatic steering without using mechanical guiding means by a guide wheel, guide rail, etc., it is important to provide means for securing safety, correcting deviations of the vehicle.
However, is no system with which above mentioned problems are solved sufficiently by a compact and weight saving construction and effective high speed operation can be made possible.
The inventors proposed in Japanese Patent Application No. 2005-148401 (patent literature 2) a tramway transit system with fail-safe function in which the vehicle is provided with a steering mechanism for automatically steering the vehicle by means of an actuator and guard wheels which do not contact a protection track laid down along the track when the vehicle is traveling under automatic steering. The system is provided with a fail-safe means so that when abnormal circumstances occur the automatic steering is stopped, the guard wheels contact the protection track, and the vehicle is steered via the guard wheels contacting the protection track.
In Japanese Patent No. 3185512 is disclosed an automatic steering device, in which a manual and automatic input system of steering force are connected parallel to a steering force control system of a power steering mechanism, and when the driver of the vehicle inputs a steering force larger than a automatically applied steering force, steering by the driver is prioritized.
In the patent literature 2, when malfunction occurs in the steering mechanism and the guard wheels contact the protection track, reaction force the guard wheels receive from the protection track is transmitted to the steering mechanism. The actuator disclosed in the patent literature 2 consists of an electric motor, a ball screw type feed mechanism connected to the output shaft of the electric motor, and a deed nut member engaged with the ball screw. An actuation rod for steering the wheels is connected to the feed nut member. The actuator of this construction is simple in structure, however, large reaction force exerts on the guard wheels and steering mechanism when the guard wheels contact the protection track caused by malfunction of the steering mechanism or disturbances, which may induce damage of the guard wheels or occurrence of deformations of constituent parts of the steering mechanism and shorten the life of the guard wheels or add to wear of the constituent parts of the steering mechanism.
The actuator of the automatic steering mechanism of the patent literature 3 adopts oil hydraulic servo cylinder. With the actuator of this type, reaction force due to contact of the guard wheels with the protection track when malfunction occurs in the steering mechanism can be reduced by providing a relief valve. However, a hydraulic circuit including a hydraulic pressure generator, working oil storage tank, and control valve is required to be provided. Therefore, a large underfloor space is required to accommodate these devices including piping, maintenance of the devices and piping is necessary, and particularly care and attention must be paid concerning oil leaks.
Further, when an air servo cylinder is adopted for the actuator of the automatic steering mechanism, a large air tank and high performance air compressor are required. As air pressure obtainable is about one tenth of that of oil, an air cylinder of large size must be adopted and larger space for accommodating devices is required.
Reaction force the guard wheels receive from the protection track when the guard wheels contact with the protection track caused by malfunction of the steering mechanism or disturbances can be reduced by lowering pressure in the air circuit, however, retard in controlling tends to occur. Further, steering by means of guard wheels when malfunction occurs in the steering mechanism is unstable as is in the case of the oil hydraulic servo cylinder.